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P0171, P0174 Codes

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My car is a 03 Boxster 2.7 (56000 miles)

I have a Durametric cable.

Since two months I'm having CEL. The fist time the CEL show up, I had P0171 and P0300 series. P0300 is ok now because I changed all 6 ignition coils that were lightly cracked. This morning, P0171 shows up again and a new one, P0174.

I'd notice that everytime (3x) CEL shows up, it is when engine is warm and when I'm about to park the car and motor is at iddle. CEL never happen when on the road... At iddle, RPM is very steady, engine Rev fine and very smootly.

I did check the entire intake piping from the MAF to the throttle body and from throttle body to motor intake. Everything is tight. So I'm out of idea. Any other think to check for or maybe a cure?



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P0171 Oxygen Sensing Adaptation, Idle Range, Bank 1 – Above Limit

P0174 Oxygen Sensing Adaptation, Idle Range, Bank 2 – Above Limit

Possible fault causes:

- Incorrect signal from MAF sensor

- Intake air system leaking

- Fuel pressure too low

- Volume supply of fuel pump too low

- Fuel injectors fouled

- PCV valve leaks

- Cap of oil filler neck not closed correctly or seal is damaged

Looks like you have a leak...

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Other that piping from the MAF and throttle body, where do i have to check for a leak?

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Did you see the list?

Did you have the oil filler cap off? The oil filler tubing gets brittle as it gets older and is easily cracked.

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Ok, did look into the engine section for a leak search and found a white&black round part that have two small hoses going in by a "Y" but the ouput of the part in not plugged. Normal or no? Please look at att. picture.


post-1-055312500 1276616830_thumb.jpg

Edited by Loren
made image viewable here

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Ok, I found where that backflow goes. it is in the right rubber sleave that att. the throttle body to the right intake plenum. There is a hole there to plug the output of that black/white valve.

So Loren, I guess, that's the source of my leak! What do you think?

I'll reset my CEL and see the result.

Thanks for the help.


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This is my final update. I did it! That check valve was out of his plug and it was a source of two problems: 1- Repetitive CEL P0171 & P0172 and 2-Short hiccup when pushing on gas at low RPM.

I'm so happy! My car is now like new!



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